Process for preparing o,o-dialkyl, s-n-alkyl-carbamylmethyl phosphorodithioates



PROCESS FOR PREPARING 0,0-DIALKYL, S-N- ALKYL-CARBAMYLMETHYL PHOSPHORODI- THIOATES Mario Perini and Giovanni Speroni, Milan, Italy, as-

signors to Montecatini Societa Generale per llndustria Mineraria e Chimica, Milan, Italy N Drawing. Filed Jan. 15, 1957, Ser. No. 634,181

5 Claims. (Cl. 260-461) This invention relates to parasiticidal formulations containing, as active substances, alone or in mixture with other active substances, certain specific and selected N- alkylamides of 0,0-dialkyldithiophosphorylacetic acids which we have found, by exhaustive research, to be exceptional among substances of the general class in having the combined properties of excellent parasiticidal activity and low toxicity to warm-blooded animals.

As is readily understandable, in order to be of practical utility, parasiticidal materials or compositions must have no or only very low toxicity to warm-blooded animals. This is particularly true when the composition is to be used to combat pests under conditions such that it comes into i United States Patent 0 contact with food, such as fruit for instance, and there is danger that the food will be eaten while carrying a residue of the parasiticide.

N-alkylamides of 0,0-dialky1 phosphorylacetic acids of the general formula the formula, that the compounds 'as a class do not possess general pest-control characteristics and that the vast majority of such compounds, even if active against some parasites, are so highly toxic to warm-blooded animals that they are unfit for incorporation in a generally useful parasiticidal composition.

Our investigations reveal, further, that the various substituents in the general formula given must be selected and specific, in order for the compound to have the desired parasiticidal activity coupled with low toxicity to warm-blooded animals.

Only three compounds embraced in the general formula have been found by us to have the required combination of properties; high parasiticidal activity and low toxicity to warm-blooded animals. These are the following substances;

N-monoisopropylamide or 0,0-dimethy1dithiophosphorylacetic acid N-monomethylamide of 0,0 dimethyIdithiophosphorylacetic acid It will be observed that, in these three compounds, the

atom corresponding to X in the general Formula A is a sulfur atom. This is-extremely important because ifsuclk atom is an oxygen atom, then the toxicity of the compound to warm-blooded animals is markedly increased, withoutany corresponding increase in the parasiticidal activity, as proved by the following:

When the acute toxicity per us of our Compound I is made equal to 1.0 as determined on mice, the correspond-. ing toxicity per os of the compound OCzHa CHUJHID O=P-SCH2CO-N CgH is found to be 2.5.

The character of the substituents R and R in Formula A also exerts an influence on the toxicity of the compounds. This is evidentfrom Table I below in which the acute toxicities per os we have found for various other compounds included in the general formula (A) are compared with those of our selected and specific compounds, the N-isopropylamide and N-monomethylamide of 0,0- dimethyldithiophosphorylacetic acid, the toxicity per 0s 7 of the two last-mentioned compounds being taken as 1.0,

for a standard of comparison.

3 TABLE IContinued gen linked to P, and the chemical nature and molecular structure of the substituents R and R is apparent from Acute Nuimide toxicity 21 consideratton of the values given 1n Table I. Thus, it 1s p 05 seen that even the presence of two methyl groups on the N atom, instead of a single methyl group and a hydrogen CaHs C 2 4 atom, has the effect of increasing the per os tox1c1ty of the (o Y compound. We have found, also, that if either R or R 0 H is an aromatic radical, or if both R; and R are aromatic, the parasiticidal activity of the compound is practically (0 61111) 1-3- 2 i1 3 Table II below gives the results of a second screening C of the compounds and compares the activity of our speci- (0CH=)11 -SCH(?'N 1.6 fic compounds against some common parasites, and their i) om toxicity, as determined on mice, with the activity and toxicity of other known compounds.

TABLE 11 Activity Acute toxicity Compound On flies On On mites npbides (Ietrrmy- Per 05 Endov- (Aphis chus enous Topical Tarsal fabze) telarius) Psrathion (control) 1 1 1 1 1 1 1. (o,rno),1 -s-omo0111103111080 1/3 5 1/24 1/21 2. (CH;O):]P1SCHr-CONH-CH; 1/3 1/4 1/4 1 1/5.9 1/00 a. (GHgOME-S- CHr-QQNHmHmso) 1/10 1/20 1.5 10 1/10 1 14 N 4. (C|Ht0)zfi-0 N 1/3 1/3 1/10.6 1/16.8

5. [CHs(CH2)3O] -PSCH2-CONHi-u 1/1,250 1/1,s00 1/250 1 100 1/100 1 :10

0. (CeHgOhliSCHzCONH: 1/1,250 1/6,250 1/300 1/100 1/134 1/211 7. (C:H.-,0)z1lTSCHrCONH 1/1,250 1 0,250 1 100 1 250 1/500 1/61 8. (C H;O),l|Fl SCH:CH;CONH. 1/1,000 1/1,s00 1/250 1 400 1/140 1 44 The fundamental influence of the substituents on the practical utility of the compounds, including that of oxy- Table III gives the biological activity to toxicity ratios found for the compounds shown in Table II.

TABLE IlL-continned On On mites Compound On flies aphides (Tetra- (Aphis nychus fabae) telarius) a. [oHnoHmomr-s-om-cONE, 0.006 0.04 0.11 .s stmmon-rr-s-om-oorsn: o.o21 o.45 1. a4 a In. s c zrmumn-tg-s-om-oomrG -o. s 2

8. (CzH 0)z-1gS-CHe-CHn-CONHC}.-. 0.0a 0.56 0.35

It is obvious from the foregoing that our Compounds I-III are uniquely useful as parasiticides or in parasiticidal compositions under any conditions where low toxicity to warm-blooded animals is a criterion Those compounds are in fact, excellent parasiticides, by which we mean they are substances or agents whieh'actively control ani-- rnal parasites such as, for example,

We have found by actual test that formulations comprising, as active parasiticide, N-isopropylamides of 0,0- dimethyL'and 0,0-diethylphosphorylacetic acid, are not only efiective for the control of various species of parasite including those belonging to the order listed above, but that such formulations exhibit special activity against all mites, in all stages of their biological cycle. We have found, further, and by. actual test, that the N-monomethylamide of 0,0-dimethyldithiophosphorylacetic acid, besides having the same high general parasiticidal activity of the N-isopropylarnides of 0,0-dimethyl and 0,0-diethyl-dithiophosphorylacetic acids, is especially active against Musca domestica and has a particularly low toxicity to warm-blooded animals, as is discussed and demonstrated more in detail hereinbelow.

The specific parasiticidal activity of our compounds is-illustrated in the following tabulations of the results of our tests. In these tabulations, the compounds are designated I, II and III (see formulae above) for conyenience.

- (1) Activity against Tetranychus telarius (a) By nebulizing a mixed population of mites in variout stages of growth on bean plants under standardized conditions with an aqueous dispersion of Compounds I-III, the following average mortalities were observed, at the twenty-fourth hour:

TABLE IV.--SPECIFIC ACTIVITY AGAINST T ETRAN YCH US TELARI US Concentra- Percent tion, percent Percent mortality Formulatlonbasedoncompound active mortality with equal substance doses of (11.8.) U Parathlon at: a m 0. 001 to 0.0005 35 (b) By nebulizing mite eggs, the following average mortalities were obtained (as measured 5 days after treatment):

TABLE V.ACTIVITY AGAINST- EGGS OF 7 TETRANYCHUS TELARIUS Concentra- Percent Formulation based on compound tionkpgrcent mortality (c) A test carried out on eggs of Tetranychus t. laid within 3 days on apple-tree leaves, which were subsequently sprayed under standardized conditions as hereunder indicated, gave the following results:

- (2) Activity against Aphis fabae By nebulizing a population of aphides, apterous virginoparous females, on bean plants under'standardized. conditions with suitably formulated aqueous dispersions 7 of Compounds I-III, the following average mortalities were obtained after 24 hours:

TABLE VII.ACT I VIT Y AGAINST APHIS FABAE Percent Concentra- Percent mortality Formulation based on compound tion, percent mortality with equal AB. doses of Parathion 0. 005 100 99 I 0. 004 100 0.002 60 0. 001 25 65 0. 005 100 99 H 0. 004 100 0. 001 85 65 0. 0005 10 8365 88 88 m 0. 004 75 en 0. 001 65 (3) Activity against Musca domestica (a) By topical application, by means of a microsyringe, of acetone solutions of Compounds I-III to five day old female flies, the following average percent mortalities were obtained after 20 hours:

TABLE VIII.ACTIVITY AGAINST MUSCA DOMESTICA [TOPICAL APPLICATION] Gamma Percent Formulation based on compound A.S. mortality per fly 1 100 I. 0. 5 97 0. 4 81 0.4 100 It 0. 3 99 0.2 75 is 32 m 0.06 65 0.05 31 (b) On tarsal absorption, after removal of the solvent, by introducing five day old female flies into a beaker perviously treated with controlled amounts of benzene solutions of Compounds I-III, and leaving the flies in contact with these substances for 20 hours, the following mortalities were observed:

TABLE IX.-ACTIVITY AGAINST M USCA DOMESTICA (4) Activity against Acyrthosiphon onobrychis By spraying under standardized conditions broad-bean plants infested by this kind of aphides with aqueous dispersions of Compounds II-III, the following results were obtained:

TABLE X.'-ACTIVITY AGAINST ACYRT H OSI- PHON ONOBRYCHIS Formulation based on Conceutra- Percent DL compound tion, p.p.m., mortalit; p.p.m.,

A.S. h AB 1. 5 12. 3 8 2. 0 30.5 H 2. 5 a9. 0 3. 8 67. 7 4. 6 73. 4 4 1g. 5 8 4 5 m 15 77. 4 30 97. 3

(5) Activity against Drosophila melanogaster The test was carried out by forming uniform deposits of the insecticides under examination through evaporation of the solvent of their solutions in Petri boxes. The results obtained by plotting the action lines for the compounds considered and for the comparison compounds are the following:

TABLE XI.ACTIVITY AGAINST DROSOPHILA MELANOGASTER p DL after Relative Formulation based on compound hrs. in activity I (Parathion=1) Parathion 0. 55 l.

(6) Activity against Culex pipiens By dipping the third-aged larvae of these insects in suitably formulated aqueous dispersions of Compounds II, III, the following average mortalities were obtained after 24 hours:

TABLE XII.--ACTIWTY AGAINST CULEX PIPIENS Formulation based on compound A.S., Percent p.p.m. mortality III 6 98 Moreover, substance I (N-monoisopropylamide of diethyldithiophosphorylacetic acid) has proved as extraordinarily effective against the following parasites:

TABLE XlII.--RESULTS OF FIELD TESTS Concentra- Percent Parasite tion A.S. mortality (pip. (aftcrzfi thousand) hours) Paratetranychus pilosua g Heliathripr h'remarroirlnlis (on snowball-tree) 0.1-0.2 100 Tingis' part (on apple-tree) 0.1-0.2 I00 Hywlapteroux arumiinis (on peach-tree) 0.16 -100 Aphis point (on apple-tree) 0 2 10,0 Myrus terasr 0 2 1 Adults. 1 Eggs.

Determination of the acute toxicity (to warm-blooded animals) per os.--The acute toxicity per as was deter mined by gastric sounding and by administration of solutions of the product considered in dimethylacetamide to white mice size 18/20 g. The interference of the solvent with the toxic phenomena is to be considered as negligible.

9 TABLE XIVi-ACUTE TOXICITY PER Our Compounds I-III can be prepared by'the methods known for the preparation of S-substituted derivatives of 0,0-dialkyl dithiophosphoric acids. For instance, the products can be formed by reacting an alkaline salt of the acid with an N-methyl-alpha-haloacetamide, in'the pres- 'ence of an organic solvent for the two reactants. ,However, the products resulting from such reaction under the known conditions are impure. Since the purity of the product used'as parasiticide is of extreme importance, inasmuch as the contaminating substances occuring therewith have poor activityaga'inst parasites, the products of the methods mentioned must be subjected to purifying after-treatments. I V

- We have developed aspecial and improved method of preparing our Compounds I-III which results directly in pure products which do not require further purification steps. In accordance with our method, the reaction between the alkaline salt of the acid and the N- methyl-alpha-haloacetamide is. carried out, at a temperature between C.,and C., in water or in a mixture of water and of an organic solvent miscible therewith, including monohydric loweraliphatic alcohols such as methanol and ethanol, low molecular weight ketones including acetone, glycols, dioxane, etc.

The following examples illustrate our method for producing Compounds I-III,'it being understood that these examples are not intended as limitative since mixtures of water with other water-miscible organic solvents can be used.

EXAMPLE 1 5 kg. of crude 0,0-diethyldithiophosphoric acid are mixed with 5 liters of water, then 1250 g. of anhydrous Na CO are added at a temperature not higher than 30 C, while stirring. Stirring is continued for half an hour, after which the solution is cooled to 10 C. The liquid is filtered and the oil layer is separated. The water solution of the sodium salt of diethyldithiophosphoric acid is now added rapidly, while cooling moderately to maintain the reaction mass at a temperature of about 10 C., to a mixture of 2900 g. N-isopropylchlorocetamide and 7 liters of water. Stirring is continued and the above temperature is maintained for hours. The oily phase is then separated and shaken with a sodium bicarbonate solution if the pH is acidic, or with a carbon dioxide solution if the pH is alkaline, until pH 7 is reached. After separating it from water, the oil is now dried at 70-80 C. under vacuum. 4500 g. of monoisopropylamide of 0,0-diethyldithiophosphorylacetic acid are thus obtained. The product comes as straw-colored crystals, melting point 23-24 C., boiling point 152-155 C. at 0.1-0.2 mm. Hg, insoluble in water and soluble in numerous organic solvents including monohydric aliphatic alcohols such as ethanol and methanol, aliphatic ethers such as ethyl ether, ketones, and aromatic hydrocarbons of low molecular weight such as benzene, toluene, etc.

if the process is carried out using an organic solvent, such as acetone, instead of water, the product comes as a brown-colored oil of low purity.

EXAMPLE 2 80 g. of crude 0,0-dimethyldithiophosphoric acid in 135 cc. water are neutralized to pH 7 with about 31 g. potassium carbonate. The mixture is filtered and the solidscollected are washed twice with 70 cc. water in total. The oil drops which settle in the filtrate are separated. The oily phase is discarded. The aqueous solution is transferred to a flask with 3 necks, provided with a good stirrer,'and a'solution of 38 g. monoisopropylchloroacetamide in 35 cc. acetone is added while stirring. The mass is stirred at 15 C. for at least 20 hours, then the flask is connected to a water jet suction pump and heated to 30 C. The mixture is kept at 30 C. under the maximum vacuum permitted by the apparatus (30-40 mm. Hg) for about half an hour. Then it is cooled at about 5 C. for one hour and filtered by suction; the crystals collected are washed on the filter with a small amount of water.

By collecting also the crystals which separate from the. mother liquors after 3 or 4 days, 60 g. of monoisopropyk amide of 0,0 dimethyldithiophosphorylacetic acid are obtained.

The N-monoisopropylamide of O,O-dimethyldithio-' phosphorylacetic acid is in the form of crystals which are slightly yellow colored or colorless in the pure state; melt at 7273 C., and are insoluble in water and propylene glycol, soluble in primary aliphatic alcohols and in ketones, scarcely soluble in ether, and soluble in di methylacetamide.

If the process is carried out using only acetone, in stead of the water-acetone mixture, a mixture of oily, im-. pure substance and crystals is obtained.

EXAMPLE 3 g. of crude 0,0-dimethyldithiophosphoric acid in 135 cc. of water are neutralized to pH 7 with about 31 g. potassium carbonate. The mixture is filtered and the filter is washed twice with a total of 70 cc. water. The oil drops which settle in the filtrate are separated; the oily phase is discarded. The aqueous solution is transferred to a flask with 3 necks, provided with a good stirrer, and 30.5 g. N-monomethylchloroacetamide in about 30 cc. acetone are added. The mass is stirred at 15 C. for at'least 20 hours, then the flask is connected to a water jet suction pump and heated to 30 C. The mixture is kept at 30 C. under a vacuum of 30-40 mm. Hg for about half an hour. Then, the reaction mass is cooled and dipped into about 250 cc. of cold water. The oily phase is separated and shaken with a sodium bicarbonate solution if the final pH is acidic, or with a carbon dioxide solution if the pH is alkaline, till pH 7 is reached. Finally, the mixture is allowed to separate completely and the oil obtained is clarified by filtration through pleated filters and dried under vacuum at 70-80 C. 45-48 g. of monomethylamide of 0,0-dimethyldithiophosphorylacetic acid are thus obtained, as a straw colored oil having a specific gravity at 30 C. d =1.265 and a refractive index n =l.53. This product is insoluble in water and propylene glycol and soluble in primary aliphatic alcohols, ketones, ethyl ether, and dimethylacetamide. By cooling partial crystallization takes place.

EXAMPLE '4:

178 g. of crude 0,0-dimethyldithiophosphoric acid suspended in 170 cc. of water are neutralized with 54 g. sodium carbonate. The mixture is filtered and the filter is washed twice with a little water. The oil drops which settle in the filtrate are separated and discarded. The aqueous solution is transferred to a flask with 3 necks, provided with stirrer, and 70 g. of N-monomethylchloroacetamide in about 470 cc. water are added. The mass is stirred at 15 C. for at least 36 hours, then g. sodium chloride are added. After stirring for another 8 hours, the mass is agitated for 1 hour with 60 cc. carbon tetrachloride. The oil layer is then separated, washed with 50 cc. water, neutralized with sodium bicarbonate to pH 7 and finally distilled under vacuum at a temperature not higher than 50 C.

g. of monomethylamide of 0,0-dirnethyldithiophosphorylacetie acid are thus obtained, in the form of an oil, which by cooling to below 20 C. crystallizes almost completely. The solidification temperature of the mass is 22-23 C.

If the process is carried out using acetone, instead of water, as a solvent, the product comes as a brown oil of low purity.

It will be apparent from the data presented that the present invention, based upon the discovery and recognition of the relationship of the specific chemical structure of compounds embraced by Formula A and the capacity of the compounds to control parasites while exhibiting low toxic effects on warm-blooded animals, is an extremely valuable contribution to this art. Our Compounds I-III may be used in parasiticidal compositions under conditions for which the use of parasiticides that are toxic to warm-blooded animals is prohibited.

Some changes may be made in practicing our invention, such as changes in the conditions for making our compounds, without departing from our invention. It is to be understood, therefore, that we intend to claim as part of our invention any variations, substitutions and changes that lie within the scope of our invention and of the appended claims, and intend to include within the scope of said claims such changes as may be apparent to those skilled in the art in the practice of the principles of our invention as set forth in this specification.

What is claimed is:

1. In the production of a compound selected from the group consisting of N-monoisopropylamide of 0,0-diethyldithiophosphorylacetic acid, N-monoisopropylamide of 0,0-dimethyldithiophosphorylacetic acid, and N-monorriethylamide of 0,0-dimethyldithiophosphorylacetic acid by reaction between an alkali salt of the correspondingly dialkylated dithiophosphoric acid and the correspondingly N'alkyla'ted-alpha-haloacetamide, the improvement which comprises producing the compound directly in a pure, light-colored to substantially colorless state in which it exhibits pronounced parasiticidal activity coupled with low toxicity to warm-blooded animals without requiring purifying after-treatments, by carrying out said reaction, at a temperature between C. and C., in water.

2. In the productionof a compound selected from the group consisting of N-monoisopropylamide of 0,0-diethyldithiophosphorylacetic acid, N-monoisopropylamide of 0,0-dimethyldithiophosphorylacetic acid, and N-rnonomethylamide of 0,0-dimethyldithiophosphorylacetic acid by reaction between an alkali salt of the correspondingly dialkylated dithiophosphoric acid and the correspondingly N'-alkylated-alpha-haloacetamide, the improvement which comprises producing the compound directly in a pure, light-colored to substantially colorless state in which it ex hibits pronounced parasiticidal activity coupled with low toxicity to warm-blooded animals without requiring purify in-g after-treatments, by carrying out said reaction, at a temperature between 10 C. and 15 C., in a mixture of water and a water miscible organic solvent.

3. The method according to claim 2, characterized in that the organic solvent is a lower aliphatic alcohol.

4. The method according to claim 2, characterized in that the organic solvent is a lower aliphatic lietone.

5 The method according to claim 2, characterized in that the organic solvent is dioxane.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Pellegrinii fItali. Agn, vol. 92, No. ii, pp. 747-754 (November 1955). I

De Pietr i-T onelli: It a1. Ag'r." (Soc. Mone'catini, Signa Florence, Italy), vol. 93, No. 1, pages 49-56 (January 1956) (in Italian). 

1. IN THE PRODUCTION OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF N-MONOISOPROPYLAMIDE OF O,O-DIETHYLDITHIOPHOSPHORYLACETIC ACID, N-MONOISOPROPYLAMIDE OF O,O-DIMETHYLDITHIOPHOSPHORYLACETIC ACID, AND N-MONOMETHYLAMIDE OF O,O-DIMETHYLDITHIOPHOSPHORYLACETIC ACID BY REACTION BETWEEN AN ALKALI SALT OF THE CORRESPONDINGLY DIALKYLATED DITHIOPHOSPHORIC ACID AND THE CORRESPONDINGLY N-ALKYLATED-ALPHA-HALOACETAMIDE, THE IMPROVEMENT WHICH COMPRISES PRODUCING THE COMPOUND DIRECTLY IN A PURE, LIGHT-COLORED TO SUBSTANTIALLY COLORLESS STATE IN WHICH IT EXHIBITS PRONOUNCED PARASITICIDAL ACTIVITY COUPLED WITH LOW TOXICITY TO WARM-BLOODED ANIMALS WITHOUT REQUIRING PURIFYING AFTER-TREATMENTS, BY CARRYING OUT SAID REACTION, AT A TEMPERATURE BETWEEN 10* C. AND 15* C., IN WATER. 